1. Field of the Invention
The present invention relates generally to the field of biometrics.
2. Background Art
Biometrics is a science involving the analysis of biological characteristics. Biometric imaging captures a measurable characteristic of a human being for identity purposes. See, e.g., Gary Roethenbaugh, Biometrics Explained, International Computer Security Association, Inc. (1998), pp. 1-34, which is incorporated herein by reference in its entirety.
Fingerprint scanners and palm scanners are two types of biometric imaging systems for acquiring fingerprint images and palm print images, respectively. Many fingerprint and palm print scanners include glass platens that result in latent prints. Latent print images are images of prints that remain on the platen after a person's finger or palm have been removed and may show up on subsequent images of fingerprints or palm prints acquired thereafter. To eliminate latent print images, glass platens have been replaced by platens made of silicone rubber sheets.
Commercially available silicone rubber sheets are often manufactured using a process known as calendaring. Calendaring is a rolling process in which a machine with rollers, known as a calendar, is used to form thin sheets from plastic, paper, or other materials. For silicone rubber sheets, liquid silicone is poured on rollers of the calendar with a catalyst and mixed. The rollers rotate several times. As the temperature is changed from cold to hot, the mixture begins to form a rubber sheet. The rubber sheet is then passed through another set of rollers that are very hot. The rubber sheet is then released and hardens almost instantly.
Silicone rubber sheets manufactured using calendaring often have problems associated with them. For example, they may not be completely flat, and often have inclusions and striations that cannot be removed. The silicone rubber sheets may also be cloudy in color. For many applications these characteristics may not be a problem. But in applications where the silicone rubber sheets need to be of optical quality, such as biometric imaging, commercially available silicone rubber sheets produced from calendaring do not provide adequate surface quality or finish to optimize image enhancement.
Silicone rubber molding is another process used to produce many products. However, conventional methods for molding silicone rubber also do not provide the optical quality needed for biometric imaging.
What is needed is an optical quality silicone rubber sheet that provides adequate surface quality or finish to optimize image enhancement. What is further needed is a method for making the same.